This invention relates to an anode for a fuel cell and, in particular, to an anode for a fuel cell comprised of a nickel alloy material.
Anode electrodes comprised of nickel alloy material are used in molten carbonate fuel cells. These so-called "nickel anodes" when suitably fabricated provide increased resistance to creepage, thereby helping to preserve fuel cell performance and life. Fabrication procedures for nickel anodes are disclosed in U.S. Pat. No. 5,041,159, assigned to the same assignee hereof and the teachings of which are incorporated herein by reference.
In a standard process for fabricating nickel anodes, a porous cohesive member comprised of a nickel alloy constituent is first formed. This is preferably accomplished by tape casting the member using a slurry containing the nickel alloy constituent. Typical alloy materials for the nickel alloy constituent might be aluminum, yttrium, magnesium, titanium, tantalum, molybdenum, chromium and cerium.
After tape casting, the porous cohesive member is subjected to a sintering procedure in which the nickel alloy constituent is sintered and selectively oxidized. Sintering is accomplished by subjecting the member to elevated temperatures in a preselected atmosphere. A typical temperature range for the elevated temperature might be 800.degree. C. to 1100.degree. C. and a typical atmosphere might be an atmosphere comprised of water and hydrogen in amounts providing partial pressures of the gases in a range of 25:1 to 110:1.
Following the sintering process, the sintered member is then subjected to a filling process in which the pores of the member are partially filled with a preselected amount of electrolyte material. This completes the anode electrode fabrication and the completed electrode is then assembled with other elements, including a cathode electrode element and an electrolyte tile, to form a complete fuel cell.
In the aforesaid anode electrode fabrication, the process of forming the metal alloy slurry and the processes of sintering the cohesive porous member and filling the sintered member with electrolyte are batch processes. Accordingly, the processes are costly to carry out, since each process has yield associated losses. Additionally, the sintering process results in a fragile sintered member whose thickness must be kept at or above a minimum value, typically 18 mils, to realize acceptable yields. This increases the anode material required, which adds to the overall cost of the anode.
In order to eliminate certain of these batch processes, it has been proposed to carry out the sintering and filling processes, in situ, i.e., within the fuel cell. With this method, the tape cast cohesive member is appropriately assembled in the fuel cell in the anode electrode location and the fuel cell operated. This causes the cohesive member to be subjected to an elevated temperature and to a water and hydrogen atmosphere sufficient to sinter and oxidize its nickel alloy constituent and to partially fill the pores of the sintered structure with electrolyte. While this provides the desired nickel anode electrode structure, certain undesirable effects such as, for example, unwanted sagging of the cohesive member, have been found to occur. These effects result in loss of contact and increased resistance for the anode electrode which over time, can seriously degrade fuel cell performance.
It is therefore an object of the present invention to provide a nickel anode electrode component which results in an anode electrode which does not suffer from the above disadvantages.
It is a further object of the present invention to provide a nickel anode electrode component meeting the above objective and which can be formed into an anode electrode in situ in a fuel cell.
It is a further object of the present invention to provide a method for fabricating a nickel anode electrode component meeting the aforementioned objectives.
It is yet a further object of the present invention to provide a fuel cell having a nickel anode electrode component which meets the previously mentioned objectives.